Light emitting device

ABSTRACT

The light emitting device has a light emitting diode which is made of a nitride semiconductor and a phosphor which absorbs a part of lights emitted from the light emitting diode and emits different lights with wavelengths other than those of the absorbed lights. The phosphor is made of alkaline earth metal silicate fluorescent material activated with europium.

FIELD OF THE INVENTION

[0001] The present invention relates to a light emitting deviceincluding a light emitting element, and more particularly to, a lightemitting device including a light emitting element that emits light in afirst spectrum region and a phosphor that is derived from the group ofalkaline earth metal orthosilicate or at least contains the phosphorgroup of alkaline earth metal orthosilicate, and that absorbs part oflight emitted from the light emitting element and emits light in anotherspectrum region.

BACKGROUND OF THE INVENTION

[0002] The light emitting device is, for example, an inorganic LED, anorganic LED, a laser diode, an inorganic thick film electroluminescencesheet, or an inorganic thin film electroluminescence unit.

[0003] In particular, the LED is outstanding for the characteristics ofa long life, the absence of necessity of a wide space, the strengthagainst the impact, and further for the light emission in a narrowspectrum band.

[0004] The inherent light emission from an active semiconductor materialof LED does not offer sufficiently a number of emission light colors, inparticular, a number of emission light colors with a wide spectrum band.This is true of, in particular, the case that white color light emissionis targeted.

[0005] From the state of the art, even an emission light colorunavailable originally by semiconductors can be obtained by a colorconversion technique.

[0006] The color conversion technique is essentially based on thefollowing principle: that is, at least one phosphor is disposed on anLED die; the phosphor absorbs the light emission from the die; and thenit emits photoluminescence light in another light emission color.

[0007] To compose the phosphor, basically, an organic material isavailable and an inorganic material is also available. The essentialadvantage of inorganic pigment is that it has a higher environmentresistance than an organic based phosphor. In consideration of the colorstability based on the long life of inorganic LED, the inorganicmaterial is more advantageous.

[0008] In consideration of the processing easiness, it is apparentlyadvantageous to use an inorganic fluorescent pigment instead of anorganic fluorescent coat based phosphor that requires an excessivelylong growth period to obtain a necessary film thickness. The pigment isadded into the matrix, and then placed on the LED die.

[0009] From the reason that the number of inorganic materials satisfyingthe above-mentioned demands is small, YAG group materials are, atpresent, used as the pigment for the color conversion in most cases.However, the YAG group materials have a disadvantage that they show ahigh efficiency only when the light emission maximum value is less than560 nm. Because of this, when using a YAG pigment in combination with ablue diode (450 nm and 490 nm), only a white emission light color with acold feeling can be realized. Especially, in the field of lighting,there is a higher demand concerning the color temperature and the colorreproduction. This demand cannot be satisfied by white LED's availablenow.

[0010] The International publication No. WO 00/33389 discloses thatBa₂SiO₄:Eu²⁺ can be used as the phosphor to get light close to white inusing a blue LED. The emitted light of Ba₂SiO₄:Eu²⁺ has a relativelyshort wavelength of 505 nm, and therefore, the light is remarkably incold color.

[0011] S. H. M. Poortetal., “Optical propertiesof Eu²⁺-activated”, page297 reports the properties of Ba₂SiO₄ and a phosphate such as KbaPO₄ andKSrPO₄ that are activated by Eu²⁺. In this report, it is confirmed thatthe light emission of Ba₂SiO₄ is at 505 nm. Furthermore, it is reportedthat the light emission of the two phosphates are essentially at afurther shorter wavelength (420 nm to 430 nm).

SUMMARY OF THE INVENTION

[0012] It is an object of the present invention is to provide a lightemitting device that can offer different light colors or a high colorreproducibility by the high photoluminescence effect through theremarkably good absorption of ultraviolet ray or blue ray emitted from afirst light source by a phosphor. In this case, it is particularlyadvantageous that the position of the color in the CIE-deviation ellipsecommonly used for a light source for ordinary lighting is in theextremely approximate color temperature range between about 2600K and7000K.

[0013] According to the present invention, the light emitting devicecomprises a light emitting diode which is made of a nitridesemiconductor and a phosphor which absorbs a part of lights emitted fromthe light emitting diode and emits different lights with wavelengthsother than those of the absorbed lights. The phosphor is made ofalkaline earth metal silicate fluorescent material activated witheuropium.

[0014] The phosphor may be an alkaline earth metal orthosilicateactivated by a divalent europium represented by the formula:

(2-x-y)SrO.x(Ba, Ca)O.(1-a-b-c-d)SiO₂.aP₂O₅ bAl₂O₃ cB₂O₃ dGeO₂:y Eu²⁺

[0015] (wherein 0<x<1.6, 0.005<y<0.5, and 0<a, b, c, d<0.5) and/or

[0016] an alkaline earth metal orthosilicate represented by

(2-x-y)BaO.x(Sr, Ca)O.(1-a-b-c-d)SiO₂.aP₂O₅ bAl₂O₃ cB₂O₃ dGeO₂:y Eu²⁺

[0017] (wherein 0.01<x<1.6, 0.005<y<0.5, and 0<a, b, c, d<0.5),

[0018] wherein at least one of the a, b, c, and d values is larger than0.01 advantageously.

[0019] That is, it was found out unexpectedly that the wavelength of theirradiated light is prolonged in the case a strontium silicate or amixture of a barium silicate and a strontium orthosilicate is usedinstead of a barium silicate. Substitution of silicon by germanium, andadditionally existing P₂O₃, Al₂O₃ and/or B₂O₃ influence on the lightemission spectrum. As a result, the light emission spectrum can beadjusted optimally in each case of use.

[0020] The light emitting device has, advantageously, another phosphorfrom the group of an alkaline earth metal aluminate activated bydivalent europium and/or manganese, and/or Y (V, P, Si)O₄:Eu or, afurther different phosphor for emitting a red light from the group of analkaline earth metal-magnesium-disiliate: Eu²⁺, Mn²⁺ represented by theformula:

Me_((3-x-y))MgSi₂O₃:xEu, yMn

[0021] (wherein 0.005<x<0.5, 0.005<y<0.5, and Me denotes Ba and/or Srand/or Ca).

[0022] Furthermore, it was found out that including a small amount ofmonovalent ion, in particular, a halide into a phosphor matrix isadvantageous to enhance the crystallization degree and the irradiationratio.

[0023] It is advantageous that the first spectrum region is 300 to 500nm. In this wavelength region, the phosphor of the present invention canbe well excited.

[0024] Moreover, it is advantageous that the second spectrum region is430 nm to 650 nm. In this case, a relatively pure white color can befurther obtained.

[0025] The light emitting device advantageously emits white light withan Ra value >72.

BRIEF DESCRIPTION OF DRAWINGS

[0026]FIG. 1 is a cross-sectional view showing an LED lamp in a secondpreferred embodiment according to the invention;

[0027]FIG. 2 is a cross-sectional view showing a layer structure of theblue LED in FIG. 1;

[0028]FIG. 3 shows the structure of a planar light source device in athird preferred embodiment according to the invention, wherein

[0029]FIG. 3(a) is a plan view and

[0030]FIG. 3(b) is a sectional view cut along the line A-A in FIG. 3(a);

[0031]FIG. 4 is a cross-sectional view showing an SMD (Surface MountedDiode) type LED lamp in a fourth preferred embodiment according to theinvention;

[0032]FIG. 5 is a sectional view showing an LED lamp in a fifthpreferred embodiment according to the invention;

[0033]FIG. 6 is a connection circuit diagram showing the case that aZener diode is used as an overvoltage protection element;

[0034]FIG. 7 is a connection circuit diagram showing the case that acapacitor is used as an overvoltage protection element; and

[0035]FIG. 8 is a cross-sectional view showing a semiconductor lightemitting device in a sixth preferred embodiment according to theinvention.

PREFERRED EMBODIMENTS OF THE INVENTION

[0036] In a first preferred embodiment according to the presentinvention, a light emitting device comprises two different phosphors,and in this case, at least one of the phosphors is an alkaline earthmetal orthosilicate phosphor. Thereby, the white tone can beparticularly adjusted to be accurate.

[0037] In the structural modifications of a light emitting deviceaccording to the present invention, there exist many possibilities.According to a preferred embodiment, one or more LED chips are disposedon a substrate in a reflection mirror and the phosphor is dispersed in alens disposed on the reflection mirror.

[0038] However, it is also possible that one or more LED chips aredisposed on a substrate in a reflection mirror and the phosphor iscoated on the reflection mirror.

[0039] The LED chips are advantageously filled with a transparentsealing compound with a dome-like shape. The sealing compound providesthe mechanical protection on one hand, and the sealing compound furtherimproves the optical property on the other hand (improved light emissionof the LED die).

[0040] The phosphor may be dispersed in the sealing compound. By thesealing compound, the LED chips disposed on the substrate and a polymerlens are bonded without containing a gas as much as possible. In thiscase, the polymer lens and the sealing compound have a refraction indexdifference of 0.1 at the maximum. The LED die can be sealed directly bythe sealing compound. However, it is also possible that the LED die issealed with a transparent sealing compound (i.e., in this case, thereare the transparent sealing compound and the sealing compound to containthe phosphor). Owing to the refraction indices close to each other,there is little loss of reflection at the interface.

[0041] The polymer lens advantageously has a spherical or oval dent. Thedent is filled with the sealing compound. As a result, the LED array isfixed at a short distance from the polymer lens. Thereby, the mechanicalstructure size can be reduced.

[0042] To achieve a homogeneous distribution of the phosphor, it isadvantageous that the phosphor is suspended advantageously in aninorganic matrix.

[0043] In the case that two phosphors are used, it is advantageous thatthe two phosphors are suspended in each matrix, and, in that case, thesematrices are disposed back and forth in the light propagation direction.Thereby, the matrix concentration can be reduced compared with the casethat the different phosphors are dispersed mixed together.

[0044] Next, an important step in the process of making a phosphor inthe first preferred embodiment according to the present invention willbe explained.

[0045] In producing a silicate phosphor, according to a selectedcomposition ratio, alkaline earth metal carbonate, silica dioxide, andeuropium oxide are mixed thoroughly with each stoichiometric amount asthe starting substances, and, using a conventional solid reaction usedto produce a phosphor, it is converted to a desired phosphor at 1,100°C. and 1,400° C. temperature in reducing atmosphere. In this regard, itis advantageous to add ammonium chloride or another halide of a smallratio to the reaction mixture, preferably less than 0.2 mole thereto, toenhance the crystallization degree. If required, part of the silicon maybe substituted by germanium, boron, aluminum or phosphorus, or part ofthe europium may be substituted by manganese. This can be carried out byadding a compound of above-mentioned respective elements, which will bedecomposed by heating, by a corresponding amount. In this case, thereaction condition range is maintained.

[0046] The obtained silicate emits light at a wavelength of 510 nm to600 nm, and it has a half bandwidth up to 110 nm.

[0047] By using one selected from the above-mentioned group of thephosphors or a combination of phosphors selected from theabove-mentioned group, or a combination of a phosphor of alkaline earthmetal aluminate activated by divalent europium and/or manganese, afurther different phosphor toemitared light selected from the group of Y(V, P, Si)O₄:Eu²⁺, and a conventional phosphor selected from the groupof Y₂O₂S:Eu³⁺, an emission light color with defined color temperatureand a higher color reproducibility can be obtained. This is as shown bythe following examples.

[0048] T=2778K (464 nm+Sr_(1.4)Ba_(0.6)SiO₄: Eu²⁺); x=0.4619, y=0.4247,Ra=72,

[0049] T=2950K (464 nm+Sr_(1.4)Ba_(0.6)SiO₄: Eu²⁺); x=0.4380, y=0.4004,Ra=73,

[0050] T=3497K (464 nm+Sr_(1.6)Ba_(0.4)SiO₄: Eu²⁺); x=0.4086, y=0.3996,Ra=74,

[0051] T=4183K (464 nm+Sr_(1.9)Ba_(0.08) Ca_(0.02) SiO₄: Eu²⁺);x=0.3762, y=0.3873, Ra=75,

[0052] T=6624K (464 nm+Sr_(1.9)Ba_(0.02)Ca_(0.08)SiO₄: Eu²⁺); x=0.3101,y=0.3306, Ra=76,

[0053] T=6385K (464 nm+Sr_(1.6)Ba_(0.4)SiO₄: Eu²⁺+Sr_(0.4)Ba_(1.6)SiO₄:Eu²⁺); x=0.3135, y=0.3397, Ra=82,

[0054] T=4216K (464 nm+Sr_(1.9)Ba_(0.08)Ca_(0.02)SiO₄: Eu₂₊); x=0.3710,y=0.3696, Ra=82,

[0055] 3954K (464 nm+Sr_(1.6)Ba_(0.4)SiO₄: Eu²⁺+Sr_(0.4)Ba_(1.6)SiO₄:Eu²⁺+YVO₄: Eu³⁺) ; x=0.3756, y=0.3816, Ra=84,

[0056] T=6489K (464 nm+Sr_(1.6)Ba_(0.4)SiO₄: Eu²⁺+Sr_(0.4)Ba_(1.6)SiO₄:Eu²⁺+barium magnesium aluminate: Eu²⁺); x=0.3115, y=0.3390, Ra=66,

[0057] T=5097K (464 nm+Sr_(1.6)Ba_(0.4)(Si_(0.08)B_(0.02)) O₄:Eu²⁺+Sr_(0.6)Ba_(1.4)SiO₄: Eu²⁺); x=0.3423, y=0.3485, Ra=82,

[0058] T=5084K (464 nm+Sr_(1.6)Ba_(0.4)(Si_(0.08)B_(0.02)) O₄:Eu²⁺+Sr_(0.6)Ba_(1.4)SiO₄: Eu²⁺+strontium magnesium aluminate: Eu²⁺);x=0.3430, y=0.3531, Ra=83,

[0059] T=3369K (464 nm+Sr_(1.4)Ba_(0.6)Si_(0.95)Ge_(0.05)O₄: Eu²⁺);x=0.4134, y=0.3959, Ra=74,

[0060] T=2787K (466 nm+Sr_(1.4)Ba_(0.6)Si_(0.98)P_(0.02)O_(4.01): Eu²⁺);x=0.4630, y=0.4280, Ra=72,

[0061] T=2913K (464 nm+Sr_(1.4)Ba_(0.6)Si_(0.98)Al_(0.02)O₄: Eu²⁺);x=0.4425, y=0.4050, Ra=73.

[0062] In one advantageous embodiment according to the presentinvention, the color conversion may be performed as below.

[0063] One or more LED chips are assembled on a substrate. Directly onthe substrate, a sealing material is disposed formed semispherically ora semielliptically (for the purpose of protecting the LED chipprotection on one hand, and for the purpose of well and for emittingpreferable discharge of the light generated in the LED chips on theother hand). The sealing material may separately seal each die, or itmay be commonly formed for all the LED's. The substrate thus fabricatedis disposed in a reflection mirror or the reflection mirror is placed onthe LED chips.

[0064] A lens is installed on the reflection mirror. On one hand, thelens is used for protecting the device, and on the other hand, afluorescent pigment is mixed in the lens. Thereby, the lens gives animpression of an opaque and yellow color. Blue light (includingultraviolet ray) passed through the lens is converted to a longerwavelength light (yellow light) when passing through the optical parts.As a result, a white color impression can further be obtained by mixingthe blue light and converted light (yellow light). For example, the lossby the waveguide effect generated between flat and parallel plates canbe reduced by the opaqueness and the dispersion property of the lens.Further, by the reflection mirror, only the preliminarily adjusted lightis controlled to be entered into the lens. As a result, the totalreflection effect can be reduced from the beginning.

[0065] Alternatively, the reflection mirror may be placed on each LEDchip, and the reflection mirror is filled in a dome-like shape, andfurther, the lens is disposed above each reflection mirror or above theentire device.

[0066] It is advantageous to use an LED array instead of a single LED inthe production of the light emitting device for illumination. In anotheradvantageous embodiment of the present invention, the color conversionmay be executed by the LED array with the LED chips assembled directlyon a substrate as follows.

[0067] Using a sealing compound (such as an epoxy resin), an LED arrayis bonded with a transparent polymer lens made from another material(such as a PMMA). The materials of the polymer lens and the sealingcompound are selected so as to have refraction indices as close aspossible, that is, with the phase matching. The sealing compound existsin the maximum spherical or elliptic dent of the polymer lens. The shapeof the dent is important in the point that the cover conversionsubstance is dispersed in the sealing compound. Therefore, according tothe shape, obtainment of the light emission color regardless of theangle can be ensured. In addition, the above-mentioned array can befilled with a transparent sealing compound, and further, it can bebonded with the above-mentioned polymer lens using the sealing compoundcontaining the color conversion substance.

[0068] For an LED having a particularly preferable color reproductivityusing at least two different phosphors, it is advantageous to dispersethe phosphors separately, and superimpose the same instead of dispersingthe phosphors together in one matrix. This is applied in particular to acombination for obtaining the final light emission color by a pluralityof color conversion processes. That is, the light emission color withthe longest wavelength is produced by one light emission process. Inthis case, the light emission process is carried out as follows: thatis, absorption of the LED light emission by a first phosphor, lightemission by the first phosphor, absorption of the light emission of thefirst phosphor by a second phosphor, and the light emission by thesecond phosphor. In particular, for this kind of the process, it isadvantageous to dispose the phosphors back and force in the lightpropagation direction because the concentration of the phosphors can bereduced thereby compared with the case of simply dispersing variousphosphors.

[0069] The present invention is not limited to the above-mentionedembodiments. The phosphors may be assembled in a polymer lens (oranother optical part). The phosphors may be disposed directly on the LEDdie, or it may be disposed on the surface of the transparent sealingcompound. Moreover, the phosphors may be assembled in a matrix togetherwith dispersed particles. Thereby, precipitation in the matrix can beprevented and homogeneous light emission can be ensured.

[0070] The above-described example of the use of a phosphor havingphotoluminescence effect in a light emitting diode (LED) lamp will beexplained in more detail.

[0071]FIG. 1 is a typical cross-sectional view of an LED lamp accordingto a second embodiment of the light emitting device according to theinvention. The LED lamp shown in FIG. 1 is the so-called “lens-type LEDlamp.” A blue LED 4 formed of a GaN semiconductor is mounted through amount 5 on a metal stem 3 that forms a cup 10 which functions as areflection mirror for reflecting, above the LED lamp, light emitted fromthe blue LED 4. One electrode of the blue LED 4 is connected to a leadframe 2 through a gold bonding wire 7, and the other electrode isconnected to a lead frame 1 through a gold bonding wire 6. The inside ofthe cup 10 is filled with an internal resin 8 as a coating member to fixthe blue LED 4. Further, the lead frame 2 and the lead frame 1 providedwith the metal stem 3 are covered with an external resin 9 as a moldmember. Therefore, the blue LED 4 is double covered with the internalresin 8 and the external resin 9. The metal stem 3 and the lead frame 1are also referred to as a mount lead. The blue LED 4 will be explainedbelow in more detail.

[0072] The internal resin 8 containing a phosphor 11 is filled into thecup 10 to a level below the level surface of the upper edge of the cup10. When a plurality of LEDs are disposed close to each other in thisway, this construction can prevent mixing of colors between LEDs and canrealize a flat display using LEDs to produce images with highresolution.

[0073] Regarding the internal resin 8, a silicone resin or an epoxyresin is used which becomes transparent upon curing. The internal resin8 contains a phosphor 11 composed mainly of the divalenteuropium-activated alkaline earth metal orthosilicate and/or an alkalineearthmetal orthosilicate. As described above, the phosphor 11 hasphotoluminescence effect. Specifically, the phosphor 11 absorbs lightemitted from the blue LED 4 and emits light with a wavelength differentfrom the wavelength of the absorbed light.

[0074] Instead of the silicone resin or the epoxy resin, low meltingglass may be used as the internal resin 8. The low melting glass hasexcellent moisture resistance and, at the same time, can prevent theentry of harmful ions into the blue LED 4. Further, light emitted fromthe blue LED 4 as such can be passed through the low melting glasswithout absorption into the glass. Therefore, there is no need to emitlight with higher intensity in expectation of light absorption.

[0075] Further, a scattering material may be incorporated into thesilicone resin or epoxy resin as the internal resin 8 with the phosphor11 incorporated therein or the low melting glass with the phosphor 11incorporated therein. The scattering material irregularly reflects lightemitted from the blue LED 4 to produce scattered light. Therefore, lightfrom the blue LED 4 is more likely to apply to the phosphor 11, wherebythe quantity of light emitted from the phosphor 11 can be increased. Thescattering material is not particularly limited, and any well knownmaterial may be used.

[0076] Regarding the external resin 9, an epoxy resin may be used whichbecomes transparent upon curing.

[0077] Various resins, such as epoxy resin, may be used in the mount 5from the viewpoint of good handleability. Preferably, the resin used inthe mount 5 has adhesive properties and, in addition, has insulatingproperties from the viewpoint of avoiding, even when the mount 5 ispushed out toward the side face of the very small blue LED 4, a shortcircuit between the layers at the side face.

[0078] The mount 5 is formed of a transparent resin so that lightemitted isotropically from the blue LED 4 can be passed through thetransparent resin, reflected from the reflection mirror on the surfaceof the cup 10, and emitted above the LED lamp. In particular, when theLED lamp is used as a white light source, the color of the mount 5 maybe white which does not hinder white light.

[0079] The mount 5 may contain a phosphor 11. In the case of the LEDlamp using the phosphor 11, the optical density is much higher than thatin the case of an LED lamp not using the phosphor 11. Specifically,since light emitted from the blue LED 4 does not pass through thephosphor 11, the light emitted from the blue LED 4 is reflected from thephosphor 11 provided near the blue LED 4, is newly isotropically emittedas light excited by the phosphor 11, is also reflected from thereflection mirror on the surface of the cup 10, and is further reflecteddue to a difference in refractive index between the individual sectionsof the LED lamp. Therefore, light is partially densely confined in aportion near the blue LED 4 to render the optical density near the blueLED 4 very high, contributing to emission of light with high luminancefrom the LED lamp.

[0080] The blue LED 4 isotropically emits light, and the emitted lightis also reflected from the surface of the cup 10. These lights arepassed through the mount 5, and, thus, the optical density within themount 5 is very high. Accordingly, the incorporation of the phosphor 11into the mount 5 permits these lights emitted from the blue LED 4 to bereflected from the phosphor 11 contained in the mount 5 and to be newlyisotropically emitted as light excited by the phosphor 11 contained inthe mount 5. Thus, the incorporation of the phosphor 11 also into themount 5 can further enhance the luminance of light emitted from the LEDlamp.

[0081] Further, the mount 5 may be formed of a resin containing aninorganic material such as silver. Since a resin, such as epoxy resin,is used in the mount 5 and the internal resin 8, when the high-luminanceLED lamp is used for a long period of time, the internal resin 8 or themount 5, formed of a synthetic resin, in its portion very close to theblue LED 4 is brown or black colored and deteriorated, leading tolowered emission efficiency. In particular, the coloration of the mount5 in its portion close to the blue LED 4 significantly lowers theemission efficiency. Not only resistance to light (weatheringresistance) emitted from the blue LED 4 but also adhesion, intimatecontact and the like are required of the mount 5. The problem of thedeterioration in resin caused by light can be solved by using a resincontaining an inorganic material, such as silver, in the mount 5. Themount 5, which can meet these property requirements, can be simplyformed by mixing a silver paste and a phosphor 11 with a mount paste,coating the mixture on the metal stem 3 by means of mount equipment andthen bonding the blue LED 4 to the coating.

[0082] The mount 5 may be formed of, in addition to a silver-containingepoxy resin, a silicone resin as an inorganic material-containingorganic resin. The inorganic material contained in the mount 5 should bebrought into intimate contact with the resin, i.e., should have goodadhesion to the resin and, at the same time, should not be deterioratedby light emitted from the blue LED 4. To meet these requirements, atleast one inorganic material is selected from silver, gold, aluminum,copper, alumina, silica, titanium oxide, boron nitride, tin oxide, zincoxide, and ITO, and is incorporated into the resin. In particular,silver, gold, aluminum, copper and the like can improve heat radiationand is electrically conductive and thus can be applied to semiconductordevices expected to have electrical conductivity. Alumina, silica,titanium oxide, boron nitride and the like have high weatheringresistance and permits the mount 5 to maintain high reflectance. Theinorganic material may be in various forms, for example, spherical,acicular, or flaky form, which may be determined by taking intoconsideration, for example, dispersibility and electrical conductivity.In the mount 5, the heat radiation, the electrical conductivity and thelike may be regulated to respective various levels by varying thecontent of the inorganic material in the resin. Since, however,increasing the content of the inorganic material in the resin causes nosignificant deterioration in resin but deteriorates the adhesion, theinorganic material content is not less than 5% by weight and not morethan 80% by weight. An inorganic material content of not less than 60%by weight and not more than 80% by weight is better suited for theprevention of the deterioration of the resin.

[0083] In this way, the incorporation of an inorganic material, such assilver, which is less likely to be deteriorated upon exposure to theemitted light, into the blue LED 4, can suppress a deterioration in theresin in the mount 5 by the light. Therefore, the incorporation of aninorganic material can reduce colored sites caused by the deterioration,can prevent a lowering in emission efficiency, and can provide goodadhesion (intimate contact). The incorporation of the phosphor 11 alsointo the mount 5 can further enhance the luminance of the LED lamp.

[0084] This can realize the provision of an LED lamp which can emitlight with high luminance and causes only a very low lowering inemission efficiency even after use with high luminance for a long periodof time. Further, the use of a material having high heat conductivitycan stabilize the characteristics of the blue LED 4 and can reduceirregular color.

[0085]FIG. 2 shows the layer structure of the blue LED 4 of the LED lampshown in FIG. 1. The blue LED 4 comprises a transparent substrate, forexample, a sapphire substrate 41. For example, a buffer layer 42, ann-type contact layer 43, an n-type cladding layer 44, an MQW(multi-quantum well) active layer 45, a p-type cladding layer 46, and ap-type contact layer 47 are formed in that order as nitridesemiconductor layers, for example, by MOCVD, on the sapphire substrate41. Thereafter, a light-transparent electrode 50 is formed on the wholesurface of the p-type contact layer 47, a pelectrode 48 is formed on apart of the light-transparent electrode 50, and an n electrode 49 isformed on a part of the n-type contact layer 43. These layers may beformed, for example, by sputtering or vacuum deposition.

[0086] The buffer layer 42 may be formed of, for example, AlN, and then-type contact layer 43 may be formed of, for example, GaN.

[0087] The n-type cladding layer 44 may be formed of, for example,AlyGa1-yN wherein 0≦y<1, the p-type cladding layer 46 may be formed of,for example, AlxGa1-xN wherein 0<x<1, and the p-type contact layer 47may be formed of, for example, AlzGa1-zN wherein 0≦z<1 and z<x. The bandgap of the p-type cladding layer 46 is made larger than the band gap ofthe n-type cladding layer 44. The n-type cladding layer 44 and thep-type cladding layer 46 each may have a single-compositionconstruction, or alternatively may have a construction such that theabove-described nitride semiconductor layers having a thickness of notmore than 100 angstroms and different from each other in composition arestacked on top of each other so as to provide a superlattice structure.When the layer thickness is not more than 100 angstroms, the occurrenceof cracks or crystal defects in the layer can be prevented.

[0088] The MQW active layer 45 is composed of a plurality of InGaN welllayers and a plurality of GaN barrier layers. The well layer and thebarrier layer have a thickness of not more than 100 angstroms,preferably 60 to 70 angstroms, so as to constitute a superlatticestructure. Since the crystal of InGaN is softer than otheraluminum-containing nitride semiconductors, such as AlGaN, the use ofInGaN in the layer constituting the active layer 45 can offer anadvantage that all the stacked nitride semiconductor layers are lesslikely to be cracked. The MQW active layer 45 may also be composed of aplurality of InGaN well layers and a plurality of AlGaN barrier layers.Alternatively, the MQW active layer 45 may be composed of a plurality ofAlInGaN well layers and a plurality of AlInGaN barrier layers. In thiscase, the band gap energy of the barrier layer is made larger than theband gap energy of the well layer.

[0089] A reflecting layer may be provided on the sapphire substrate 41side from the MQW active layer 45, for example, on the buffer layer 42side of the n-type contact layer 43. The reflecting layer may also beprovided on the surface of the sapphire substrate 41 remote from the MQWactive layer 45 stacked on the sapphire substrate 41. The reflectinglayer preferably has a maximum reflectance with respect to light emittedfrom the active layer 45 and may be formed of, for example, aluminum, ormay have a multi-layer structure of thin GaN layers. The provision ofthe reflecting layer permits light emitted from the active layer 45 tobe reflected from the reflecting layer, can reduce the internalabsorption of light emitted from the active layer 45, can increase thequantity of light output toward above, and can reduce the incidence oflight on the mount 5 to prevent a deterioration in the mount 5 caused bythe light.

[0090] The half value width of the light-emitting wavelength of the blueLED 4 having the above construction is not more than 50 nm, preferablynot more than 40 nm. The peak light-emitting wavelength of the blue LED4 is in the range of 380 nm to 500 nm, for example, is 450 nm.

[0091] In the LED lamp having the above construction, upon theapplication of a voltage across the lead frames 1, 2, the blue LED 4emits blue light with a wavelength of 450 nm. The blue light excites thephosphor 11 contained in the internal resin 8, and the excited phosphor11 emits yellow light with a wavelength of 560 to 570 nm. The mixedlight, composed of blue light and yellow light, in the internal resin 8is passed through the external resin 9, and is leaked to the exterior.In this case, the mixed light is seen white to the naked eye of thehuman being, and, consequently, the LED lamp is seen as if the LED lampemits white light. Specifically, the phosphor 11 is excited by bluelight emitted from the blue LED 4 and emits light of yellow which has acomplementary color relationship with blue and has a longer wavelengththan blue. According to the invention, a more nearly pure white colorcan be produced through a combination of a plurality of phosphors.

[0092]FIG. 3 shows a structure of a planar light-source device involvinga third preferred embodiment of the light-emitting device according tothe present invention, wherein FIG. 3(a) is a plan view thereof and FIG.3(b) is a cross-sectional view cut along the line A-A of FIG. 3(a).

[0093] The planar light-source device shown in FIG. 3 is applied, forexample, to the backlight device of a liquid crystal panel. Byilluminating the liquid crystal panel from the backside thereof torender brightness or contrast to a character or an image on the liquidcrystal panel not having a light-emitting property, it enhances thevisibility of the character or the image. The planar light-source deviceis provided with and composed of the following elements.

[0094] That is, the planar light-source device comprises a transparentand substantially rectangular optical guide plate 70, a plurality ofblue LEDs 4 that are optically connected with the optical guide plate 70by being arranged in an array and buried in a side of the optical guideplate 70, a light reflecting case 71 for reflecting light whichsurrounds other faces than a light-emitting face 70 a of the opticalguide plate 70 and fixed to the optical guide plate 70, a lightscattering pattern 73 comprising systematic and fine convex-concavepatterns formed on a light reflecting face 72 opposing to thelight-emitting face 70 a of the optical guide plate 70, a transparentfilm 74 being fixed to the optical guide plate 70 such that thelight-emitting face 70 a is covered, and containing a phosphor 11 insidethereof.

[0095] Further, each of the blue LEDs 4 is fixed to the light reflectingcase 71 such that driving voltage of a predetermined voltage is suppliedvia a power supplying means such as a bonding wire and a lead frame froma power source. The light scattering pattern 73 is provided to scatterthe light emitted from the blue LEDs 4 in the inside of the opticalguide plate 70.

[0096] In the planar light-source device composed like this, whendriving voltage is applied to each blue LED 4, light is emitted fromeach blue LED 4, which was driven. The light emitted travels within theoptical guide plate 70 towards a predetermined direction and collideswith the light scattering pattern 73 formed on the light reflecting face72, whereby being reflected and scattered, the light is emitted from theemitting-face 70 a through the film 74 as planar emitting-light. Part ofthe light emitted from the blue LEDs 4, when it passes through the film74, is absorbed by the phosphor 11, and simultaneously with this, thewavelength conversion thereof is performed to be emitted. This resultsin that a color of the emitted light, which is observed from the frontof the film 74, becomes a resultant color mixed with such light, forexample, white as the above-mentioned principle. Like this, according tothe planar light-source device of the third preferred embodiment, thelight emitted from the blue LEDs 4 is inputted into the optical guideplate 70, then the inputted light, while being reflected to scatter bythe light scattering pattern 73 formed on the reflecting face 72 of theoptical guide plate 70, is emitted from the emitting face 70 a to thefilm 74, and in the film 74, the light is partly absorbed by thephosphor 11, and at the same time, the conversion of wavelength thereofis performed to be emitted. Therefore, it is possible to make the colorof the emitted light white, without using LEDs of each color of red,green and blue as in conventional cases, with blue LEDs 4 only.Moreover, in this structure, since the phosphor 11 and the blue LED 4 donot directly contact to each other, the deterioration of the phosphor 11can be suppressed for a long period, whereby a predetermined color toneof the planar light source can be held for a long period.

[0097] Besides, by changing the kindof the phosphor 11 to be containedin the film 74, it becomes possible to realize a color of the emittedlight of not only white but also other colors. If the fixing structureof the film 74 is made a readily removable one, and a plural kinds offilms 74 each containing different kind of phosphor 11 from the othersare prepared, the color tone of the planar light source can be easilyvaried by only changing the film 74.

[0098] Further, the phosphor 11, besides the method to make it containedin the film 74, may be coated on the film 74, and in this case, also, asimilar effect to that in the case of being contained can be obtained.

[0099] Furthermore, although the blue LED 4 are optically connected withthe optical guide plate 70 by being buried into the optical guide plate70, besides this, the blue LED 4 and the optical guide plate 70 may beoptically connected by adhering the blue LED 4 to the end face of theoptical guide plate 70, or by guiding the light emitted from the blueLED 4 to the end face of the optical guide plate 70 with an opticaltransmission means such as an optical fiber. Moreover, the number of theblue LED 4 to be employed may be made to one.

[0100]FIG. 4 shows an LED lamp of SMD (Surface Mounted Device) typeinvolving a fourth embodiment of the light-emitting device according tothe present invention.

[0101] The SMD-type LED lamp has a structure as described below. A metalframe is formed by two wiring patterns of gold 81 and 82 covering theboth surfaces of a substrate 80 of glass epoxy resin with an insulatingproperty, and being formed to be electrically separated from each other.Over the wiring patterns 81 and 82, a frame 83 having a plastic-made cup83 a is provided. The surface of the cup 83 a constitutes a reflectionmirror, which reflects light emitted from the blue LED 4. The wiringpattern 81 and 82 are not symmetrical. The upper surface of the wiringpattern 82 is formed as far as the center of the bottom of a spaceformed by the frame 83, while the other wiring pattern 81 is exposed alittle to the bottom of the space formed by the frame 83.

[0102] The blue LED 4 is adhered firmly to the upper surface of thewiring pattern 82 with epoxy resin paste containing silver filaments. Ap-electrode of the blue LED 4 and the wiring pattern 82 are connectedwith a bonding wire of gold 6, and an n-electrode of the blue LED 4 andthe wiring pattern 81 are connected with a bonding wire of gold 7.

[0103] The inside of the space formed by the cup 83 a of the frame 83 isfilled with a sealing material 88 which becomes transparent after cakingthereof. The blue LED 4 is fixed by the sealing material 88. The sealingmaterial 88 contains the phosphor 11 mainly composed of alkaline earthmetal orthosilicate activated by bivalent europium and/or alkaline earthmetal orthosilicate. The sealing material 88 comprises epoxy resin orsilicone resin. The sealing material 88 containing the phosphor 11 maybe filled in the whole space formed by the cup 83 a of the frame 83, ormay be filled up to a position below the upper edge of the frame 83.

[0104] Meanwhile, the sealing material 88 containing the phosphor 11 mayfurther contain a scattering material. The scattering material causesirregular reflection of the light emitted from the blue LED 4, whichchanges the light to scattered light. Consequently, the light from theblue LED 4 becomes easy to strike the phosphor 11, whereby quantity oflight to be emitted from the phosphor 11 can be increased. Thescattering material is not limited to any particular one, but well-knownscattering materials can be used.

[0105] In the SMD-type LED lamp composed like this, when a voltage isapplied between the wiring patterns 81 and 82, the blue LED 4 emit bluelight having a wavelength of 450 nm. The blue light excites the phosphor11 contained in the sealing material 88, and the excited phosphor 11emits yellow light of 560 to 570 nm. The mixed light constituted of theblue light and the yellow light in the sealing material 88 comes throughthe sealing material 88 to the outside thereof, which looks white tohuman eyes. As a result, the LED lamp looks as if it were emitting whitelight. That is, the phosphor 11 is excited by the blue light emittedfrom the blue LEDs 4, and emits yellow light which is in a complementarycolor relation with blue and having a longer wavelength than that ofblue. According to the present invention, by combining a plurality ofphosphor, white light which is nearly pure white can be obtained.

[0106]FIG. 5 is a schematic diagram showing an LED lamp according to afifth preferred embodiment of a light emitting device of the presentinvention. In the present embodiment, a blue LED 4 is arranged in suchthat it can be protected from over voltage of static electricity and thelike, and a constitution of which is the one wherein an overvoltageprotection element 91 is added to a light source shown in FIG. 1.

[0107] As shown in FIG. 5, the overvoltage protection element 91 isfabricated in a chip having a size substantially equal to that of theblue LED 4, and the protection element is located in between the blueLED 4 and a mount 5. In the present embodiment, the blue LED 4 ismounted in the form of flip chip different from the case of FIG. 1 fromthe reason mentioned later. The overvoltage protection element 91 isprovided with electrodes 92 and 93 for connecting with the blue LED 4and a lead frame 1. The electrode 92 is located at a position opposed tothat of the p-electrode 48 shown in FIG. 2, while the electrode 93 islocated at a position opposed to that of the n-electrode 49.Furthermore, the electrode 93 is formed so as to extend to a side of theovervoltage protection element 91 in order to be easily connected with abonding wire 6. The electrodes 92 and 93 on the overvoltage protectionelement 91 are connected with the p-electrode 48 and the n-electrode 49of the blue LED 4 through Au bumps 94 a and 94 b, respectively. Theovervoltage protection element 91 may be a Zener diode, which isenergized in the case when a voltage more than a specified voltage isapplied, or a condenser, which absorbs pulse voltage, and the likecomponents.

[0108]FIG. 6 is a connection circuit diagram showing a case wherein aZener diode is used for the overvoltage protection element 91. The Zenerdiode 95 used for the overvoltage protection element 91 is electricallyconnected in parallel to the blue LED 4 wherein an anode of the blue LED4 is connected with a cathode of the Zener diode 95, while a cathode ofthe blue LED 4 is connected with an anode of the Zener diode 95. In thecase when an over voltage was applied between a lead frame 1 and a leadframe 2 and if the voltage is over a Zener voltage of the Zener diode95, a terminal voltage of the blue LED 4 is held by the Zener voltage,so that the former voltage does not over the Zener voltage. Thus, theblue LED 4 can be prevented from application of an over voltage, so thatthe blue LED 4 is protected from an over voltage, whereby the blue LED 4can be prevented from occurrence of device breakdown or deterioration inperformance thereof.

[0109]FIG. 7 is a connection circuit diagram showing a case wherein acondenser is used for the overvoltage protection element 91. Thecondenser 96 used for the overvoltage protection element 91 may be achip type component used for surface mount. The condenser 96 having astructure as described above is provided with belt-like electrodes onthe opposite sides thereof, and these electrodes are connected inparallel to an anode and a cathode of the blue LED 4. When an overvoltage is applied across a frame lead 1 and a frame lead 2, a chargingcurrent flows through the condenser 96 due to the over voltage to dropinstantaneously its terminal voltage, whereby an applied voltage doesnot rise with respect to the blue LED 4. Hence, the blue LED 4 can beprevented from an over voltage.

[0110] Furthermore, even when noise containing a high-frequencycomponent was applied, the condenser 96 functions as a bypass condenser,so that exogenous noise can be excluded.

[0111] As described above, the blue LED 4 has been mounted in the formof flip chip, which is turned upside down with respect to a postureshown in FIG. 1. The reason of which is in that electrical connectionsare required for both the overvoltage protection element 91 and the blueLED 4 as a result of providing the overvoltage protection element 91. Ifeach of the blue LED 4 and the overvoltage protection element 91 isconnected with the use of a bonding wire, the number of bonding wireincreases so that productivity thereof decreases, besides, since casesof contact, disconnection and the like of the bonding wires themselvesincrease, whereby there is a fear of deterioration in reliability. Thus,the blue LED 4 is mounted in the form of flip chip. More specifically,the bottom of the sapphire substrate 41 shown in FIG. 2 is located atthe uppermost position wherein the p-electrode 48 is connected to theelectrode 92 of the overvoltage protection element 91 through the Aubump 94 a, while the n-electrode 49 is connected to the electrode 93 ofthe overvoltage protection element 91 through the Au bump 94 b. As aresult, there is no need of connecting the bonding wires 6 and 7 withthe blue LED 4. In the case where the blue LED 4 is mounted in the formof flip chip, the light transparent electrode 50 shown in FIG. 2 maybereplaced by a non-light transparent electrode. Moreover, it maybearranged in such that the n-electrode 49 is thickened so as to have thesame height as that of the surface of the p-electrode 48, or a novelconductor is connected to the n-electrode 42, so that it can be used asan electrode.

[0112] As described above, according to the constitution shown in FIG.5, there is an advantage of providing no case where the blue LED 4 isdamaged or deteriorated in performance even if an over voltage isapplied due to static electricity and the like in addition to a standardadvantage as a light source in accordance with the constitution shown inFIG. 1. Furthermore, since the overvoltage protection element 91functions as a submount, even if the blue LED 4 has been mounted in theform of flip chip, there is no case of lowering a height of bondingpositions of the bonding wires 6 and 7 on the side of the chip.Accordingly, bonding can be conducted at a position substantially thesame as that of a case of the constitution of FIG. 1.

[0113] In the case where a semiconductor device is used for theovervoltage protection element 9 in FIGS. 5 and 6, a general silicondiode may be used in place of the Zener diode. In this case, the numberof silicon diodes is decided in accordance with such a manner thatpolarities of a plurality of silicon diodes are made to be the same witheach other, and they are connected in series with each other, so that avalue of a total voltage drop in forward direction (about 0.7 V× thenumber of silicon diodes) becomes equal to operating voltage withrespect to over voltage.

[0114] Moreover, a variable registor may also be used for theovervoltage protection element 91. The variable registor has such acharacteristic that its resistance value decreases with increase of anapplied voltage, whereby the variable resistor can suppress an overvoltage as in the case of the Zener diode 95.

[0115] FIG.8 shows a semiconductor light emitting device according tothe sixth preferred embodiment of the present invention.

[0116] The semiconductor light emitting device shown in FIG. 8, in whicha light emitted from a light emitting element is wavelength-convertedand radiated to the outside of a lens-shaped resin sealant, compriseslead frames 1, 2, a metal stem 3, a blue LED 4, a mount 5, bonding wires6, 7, an internal resin 8 not containing a phosphor 11, an externalresin 9, a cup 10, and further comprises a phosphor cover 100 which istransparent.

[0117] Still, the phosphor cover 100 is made of, for example, a resinbacking material containing the phosphor 11, which generatesfluorescence when the phosphor 11 is excited by a light emitted from theblue LED 4. The resin backing material is, for instance, transparentpolyester resin, acrylic resin, urethane, nylon, silicone resin,chloroethylene, polystylene, bakelite, CR39 (acryl glycol carbonateresin), etc. Since urethane, nylon and silicone resin add someelasticity to the phosphor cover 100, mounting thereof on the externalresin 9 will be easier.

[0118] Further, the phosphor cover 100 is shaped to adhere to the outersurface of the external resin 9, that is, shaped into a solidconstruction with a semispherical cover integrated into the upper partof a cylindrical cover, and mounted detachably onto the external resin9. Moreover, the phosphor cover 100 is preferably a thin film so as toreduce the light scattering due to the phosphor 11. Furthermore, thephosphor cover 100 can be fabricated relatively easily, when a resincontaining the phosphor 11 is shaped into a predetermined form byinjection molding then adhered to the external resin 9. However, thephosphor cover 100 may be fabricated by spraying a resin materialcontaining the phosphor 11 directly onto the external resin 9 and curingthe resin material, so that air gap does not appear between the externalresin 9 and the phosphor cover 100.

[0119] In the semiconductor light emitting device with the abovestructure, a light emitted from the blue LED 4 is incident to thephosphor cover 100 via the internal resin 8 and the external resin 9. Apart of the incident light is absorbed by the phosphor 11, andsimultaneously emitted to the outside after wavelength conversion.Accordingly, the color of the emitted light that is observed fromoutside the phosphor cover 100 becomes the color synthesizing thelights, such as white according to the aforementioned principle, forinstance.

[0120] Thus, according to the sixth preferred embodiment of thesemiconductor light emitting device, the light scattering due to thephosphor 11 will not occur in the internal resin 8 and the externalresin 9, because the internal resin 8 and the external resin 9, whichare resin sealants of the blue LED 4, do not contain the phosphor 11,while the phosphor cover 100 for covering the external surface of theexternal resin 9 contains the phosphor 11. Further, since the phosphorcover 100 is shaped to be a thin film, the light scattering due to thephosphor 11 is relatively small. Accordingly, by shaping the lensportion of the external resin 9 into an arbitrary form (which issemispherical in this preferred embodiment), a desired light directivitycan be obtained so that decrease in luminance accompanied withwavelength conversion can be suppressed to minimum.

[0121] Beyond that, by changing a type of the phosphor 11 that iscontained in the backing material of the phosphor cover 100, emittedlights with colors other than white can be realized. When the phosphorcover 100 has an easy-to-detach structure and several types of thephosphor cover 100 containing different types of the phosphor 11 areprepared, a color tone of emitted light can be varied easily by changingthe phosphor cover 100.

[0122] Further, the similar effect can be obtained when the phosphor 11is applied on the surface of the phosphor cover 100 instead of beingcontained in the phosphor cover 100. Moreover, since the phosphor cover100 can be mounted on a commercially available semiconductor lightemitting device, the semiconductor light emitting device can befabricated at a low cost.

Industrial Applicability

[0123] As described above, the light emitting device comprising a lightemitting element and a phosphor according to the present invention issuitable for an LED display, a backlight device, a signal, anilluminated switch, various sensors and various indicators.

What is claimed is:
 1. A light emitting device, comprising: a lightemitting element comprising a nitride semiconductor; and a phosphorwhich can absorb a part of light emitted from said light emittingelement and can emit light of wavelength different from that of saidabsorbed light, wherein: said phosphor comprises alkaline earth metalsilicate.
 2. A light emitting device wherein: said phosphor compriseseuropium-activated alkaline earth metal silicate.
 3. A light emittingdevice according to claim 1, wherein: said phosphor isdivalent-europium-activated alkaline earth metal orthosilicaterepresented by formula: (2 - x - y)SrO.x(Ba,Ca)O.(1 - a - b - c -d)SiO₂.aP₂O₅bAl₂O₃ cB₂O₃ dGeO₂:y Eu²⁺ wherein 0<x<1.6, 0.005<y<0.5, and0<a, b, c, and d<0.5, and/or divalent-europium-activated alkaline earthmetal orthosilicate represented by formula: (2 - x -y)BaO.x(Sr,Ca)O.(1 - a - b - c - d)SiO₂.aP₂O₅bAl₂O₃ cB₂O₃ dGeO₂:y Eu²⁺wherein 0.01<x<1.6, 0.005<y<0.5, and 0<a, b, c, and d<0.5, with theproviso that at least one of a, b, c, and d values is advantageouslygreater than 0.01.
 4. A light emitting device according to claim 1,wherein: said phosphor is mixed into a covering member which covers saidlight emitting element.
 5. A light emitting device according to claim 4,wherein: said covering member comprises silicone resin.
 6. A lightemitting device according to claim 4, wherein: said covering membercomprises epoxy resin.
 7. A light emitting device according to claim 4,wherein: said covering member comprises low-melting glass.
 8. A lightemitting device according to any one of claims 4 to 7, wherein: saidphosphor is mixed with a covering member which covers said lightemitting element and a scattering agent is also mixed with the coveringmember.
 9. A light emitting device according to any one of claims 4 to8, wherein: said covering member is further covered by a secondtransparent covering member.
 10. A light emitting device according toclaim 1, wherein: said light emitting element comprises a light emittinglayer containing indium.
 11. A light emitting device according to claim1 or 10, wherein: said light emitting element comprises a double heterostructure comprising a light emitting layer sandwiched between a p-typeclad layer and an n-type clad layer.
 12. A light emitting deviceaccording to claim 11, wherein: said p-type clad layer is formed ofAl_(x)Ga_(1-x)N where 0<x<1, and said n-type clad layer is formed ofAl_(y)Ga_(1-y)N where 0≦y<1.
 13. A light emitting device according toclaim 11 or 12, wherein: the band gap of said p-type clad layer islarger than that of said n-type clad layer.
 14. A light emitting deviceaccording to claim 10, wherein: said light emitting layer of said lightemitting element comprises a quantum well structure.
 15. A lightemitting device according to claim 14, wherein: said quantum wellstructure comprises a well layer of InGaN and a barrier layer of GaN.16. A light emitting device according to claim 14, wherein: said quantumwell structure comprises a well layer of InGaN and a barrier layer ofAlGaN.
 17. A light emitting device according to claim 14, wherein: saidquantum well structure comprises a well layer of AlInGaN and a barrierlayer of AlInGaN, and the band gap energy of said barrier layer islarger than that of said well layer.
 18. A light emitting deviceaccording to claim 14, wherein: said well layer has a thickness of notmore than 100 angstroms.
 19. A light emitting device according to claim1, wherein: said p-type clad layer and/or said n-type clad layer have asuperlattice structure formed stacking nitride semiconductor layers thatare different from each other or one another in composition.
 20. A lightemitting device according to claim 1, wherein: said light emittingelement is fixed onto a frame using an insulating adhesive.
 21. A lightemitting device according to claim 20, wherein: said adhesive iscolorless and transparent.
 22. A light emitting device according toclaim 20 or 21, wherein: said adhesive contains said phosphor thatcomprises a material selected from said groups of alkaline earth metalsilicates.
 23. A light emitting device according to claim 20, wherein:said adhesive is white.
 24. A light emitting device according to claim1, wherein: said light emitting element comprises a transparentsubstrate and a nitride semiconductor grown by vapor phase epitaxy onsaid transparent substrate.
 25. A light emitting device according toclaim 24, wherein: said substrate is of sapphire.
 26. A light emittingdevice according to claim 24, wherein: said light emitting elementcomprises a light reflecting layer.
 27. A light emitting deviceaccording to claim 26, wherein: said light reflecting layer is providedon a surface of the substrate opposite to the surface of the substrateon which the light emitting layer is formed.
 28. A light emitting deviceaccording to claim 27, wherein: said light reflecting layer is ofaluminum.
 29. A light emitting device according to claim 24, wherein:said light reflecting layer comprises multiple GaN-based thin layers.30. A light emitting device according to claim 1, wherein: thehalf-value width of a wavelength emitted from said light emittingelement is not more than 50 nm.
 31. A light emitting device according toclaim 1, wherein: the half-value width of a wavelength emitted from saidlight emitting element is not more than 40 nm.
 32. A light emittingdevice according to claim 1, wherein: said light emitting element has apeak emission wavelength of 380 nm to 500 nm.
 33. A light emittingdevice according to claim 1, wherein: said phosphor has a main emissionwavelength which is longer than the main peak emission wavelength ofsaid light emitting element.
 34. A light emitting device according toclaim 1, wherein: said light emitting element comprises a substantiallyrectangular light guide plate such that light emitted from the lightemitting element is introduced thereinto and is output from its lightoutput surface, and said phosphor is provided in a sheet form on thelight output surface of said light guide plate.
 35. A light emittingdevice, comprising: a light emitting element of a GaN semiconductordisposed in a cup of a mount lead; a phosphor which can absorb a part oflight emitted from said light emitting element and can emit light ofwavelength different from that of said absorbed light; a coating memberwith which the inside of said cup has been filled, said coating membercomprising a sealant containing said phosphor; and a mold member whichcovers said coating member, said light emitting element, and the tipportion of said mount lead, wherein: said phosphor comprises a memberselected from groups of alkaline earth metal silicates.
 36. A lightemitting device, comprising: a casing; a light emitting elementcomprising a LED chip which has been mounted within said casing byflip-chip bonding, said LED chip being formed of a GaN compoundsemiconductor; a phosphor which can absorb a part of light emitted fromsaid LED chip and can emit light of wavelength different from that ofsaid absorbed light; and a mold member with which the inside of the LEDchip-mounted casing has been filled, said mold member comprising atransparent sealant containing said phosphor, wherein: said phosphorcomprises a member selected from groups of alkaline earth metalsilicates, and said light emitting device radiates white light as aresult of mixing of said light emitted from said LED chip with saidlight emitted from said phosphor.
 37. A light emitting device accordingto claim 35 or 36, wherein: said light emitting element has, on its oneside, a p-side electrode and an n-side electrode and is provided on ametal frame, said p-side electrode and said n-side electrode each havebeen wire bonded by gold wire, and said light emitting element emitsblue light upon the application of a voltage supplied via said goldwire.
 38. A light emitting device according to claim 35 or 36, wherein:said light emitting element is provided within said cup, and saidphosphor is provided so as to cover said light emitting element and tolocate at a position below the upper edge of the cup.
 39. A lightemitting device according to claim 1, further comprising: a protectionelement for protecting said light emitting element from staticelectricity.
 40. A light emitting device according to claim 39, wherein:said protection element is a Zener diode or a capacitor.
 41. A lightemitting device according to claim 39, wherein: said protection elementis a submount formed of a Zener diode, and said light emitting elementis provided on said submount, and said phosphor covers the periphery ofsaid light emitting element.
 42. A light emitting device, comprising: alight emitting element of a GaN compound semiconductor provided in a cupof a mount lead; a phosphor which can absorb a part of light emittedfrom said light emitting element and can emit light of wavelengthdifferent from that of said absorbed light; and a mold member whichcovers said light emitting element and the tip portion of said mountlead, wherein: said phosphor comprises a member selected from groups ofalkaline earth metal silicates and is contained in a resin base materialconstituting a phosphor cover which covers said mold member.